Question: Which of these numbers is prime? ${37,\ 51,\ 55,\ 91,\ 96}$
A prime number has exactly two factors: 1 and itself. The factors of 37 are 1 and 37. The factors of 51 are 1, 3, 17, and 51. The factors of 55 are 1, 5, 11, and 55. The factors of 91 are 1, 7, 13, and 91. The factors of 96 are 1, 2, 3, 4, 6, 8, 12, 16, 24, 32, 48, and 96. Thus, 37 is a prime number.